Field of the Invention
The present invention relates to a diaphragm device and an optical instrument.
Description of the Related Art
For example, in optical instruments such as digital cameras and still cameras there is provided a diaphragm device that adjusts the amount of light that passes through the lens. A diaphragm device is provided with a base plate having an aperture portion, a plurality of diaphragm blades that are supported such that they are able to open and close the aperture portion, and a drive ring that causes the plurality of aperture blades to open or close. The plurality of diaphragm blades are arranged such that they are interlaced with each other along a circumferential direction. Accordingly, a structure is created in which the amount of light passing through the lens can be adjusted by adjusting the diameter of the diaphragm hole (i.e., the diaphragm aperture) that is formed by the respective diaphragm blades.
The diaphragm device is further provided with either one or a plurality of auxiliary blades separately from the diaphragm blades. The auxiliary blades are used to completely block off any aperture portion in the base plate that has not already been completely closed off by the diaphragm blades alone. The auxiliary blades are supported such that they are able to open up or close off the smallest-diameter diaphragm hole that is formed by the diaphragm blades.
Here, the diaphragm blades and the auxiliary blades are each supported by mutually independent supporting pins. The diaphragm blades and the auxiliary blades receive motive power from the drive ring and this causes them to pivot around their respective supporting pins. Because of this, the direction in which the diaphragm blades perform an opening or closing action and the direction in which the auxiliary blades perform an opening or closing action are the same direction. Based on this structure, a partition plate that separates the diaphragm blades and the auxiliary blades from each other is provided between the diaphragm blades and the auxiliary blades so as to prevent them from obstructing each other during an opening or closing operation (see, for example, Japanese Published Examined Application No. H8-328084 and Japanese Published Examined Application No. 2001-33844).
However, in the above-described conventional technology the problem arises that the size of the diaphragm device in its thickness direction (i.e., in the direction of the optical axis) is increased correspondingly to the size of the provided partition plate.